Uplink signaling for cooperative multipoint communication

ABSTRACT

A method of operating a wireless communication system is disclosed (FIG. 6). The method includes receiving a virtual cell identification (VCID) parameter (600) from a remote transmitter. A base sequence index (BSI) and a cyclic shift hopping (CSH) parameter (604,606) are determined in response to the VCID. A pseudo-random sequence is selected in response to the BSI and CSH (610,612). A reference signal is generated using the selected pseudo-random sequence (614).

This application claims the benefit under 35 U.S.C. § 119(e) ofProvisional Appl. No. 61/679,400, filed Aug. 3, 2012 (TI-72718PS) andProvisional Appl. No. 61/846,880, filed Jul. 16, 2013 (TI-74030PS),which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The present embodiments relate to wireless communication systems and,more particularly, to uplink signaling of control information in acooperative multipoint (CoMP) communication system.

Conventional cellular communication systems operate in a point-to-pointsingle-cell transmission fashion where a user terminal or equipment (UE)is uniquely connected to and served by a single cellular base station(eNB or eNodeB) at a given time. An example of such a system is the 3GPPLong-Term Evolution (LTE Release-8). Advanced cellular systems areintended to further improve the data rate and performance by adoptingmulti-point-to-point or coordinated multi-point (CoMP) communicationwhere multiple base stations can cooperatively design the downlinktransmission to serve a UE at the same time. An example of such a systemis the 3GPP LTE-Advanced system (Release-10 and beyond). This greatlyimproves received signal strength at the UE by transmitting the samesignal to each UE from different base stations. This is particularlybeneficial for cell edge UEs that observe strong interference fromneighboring base stations. With CoMP, the interference from adjacentbase stations becomes useful signals and, therefore, significantlyimproves reception quality. Hence, UEs in CoMP communication mode willget much better service if several nearby cells work in cooperation.

FIG. 1 shows an exemplary wireless telecommunications network 100. Theillustrative telecommunications network includes base stations 101, 102,and 103, though in operation, a telecommunications network necessarilyincludes many more base stations. Each of base stations 101, 102, and103 (eNB) is operable over corresponding coverage areas 104, 105, and106. Each base station's coverage area is further divided into cells. Inthe illustrated network, each base station's coverage area is dividedinto three cells. A handset or other user equipment (UE) 109 is shown incell A 108. Cell A 108 is within coverage area 104 of base station 101.Base station 101 transmits to and receives transmissions from UE 109. AsUE 109 moves out of Cell A 108 into Cell B 107, UE 109 may be handedover to base station 102. Because UE 109 is synchronized with basestation 101, UE 109 can employ non-synchronized random access toinitiate a handover to base station 102. UE 109 can also employnon-synchronized random access to request allocation of uplink 111 timeor frequency or code resources. If UE 109 has data ready fortransmission, which may be traffic data, a measurements report, or atracking area update, UE 109 can transmit a random access signal onuplink 111. The random access signal notifies base station 101 that UE109 requires uplink resources to transmit the UE's data. Base station101 responds by transmitting to UE 109 via downlink 110 a messagecontaining the parameters of the resources allocated for the UE 109uplink transmission along with possible timing error correction. Afterreceiving the resource allocation and a possible timing advance messagetransmitted on downlink 110 by base station 101, UE 109 optionallyadjusts its transmit timing and transmits the data on uplink 111employing the allotted resources during the prescribed time interval.Base station 101 configures UE 109 for periodic uplink soundingreference signal (SRS) transmission. Base station 101 estimates uplinkchannel quality information (CQI) from the SRS transmission.

Uplink (UL) cooperative multipoint (CoMP) communication requirescoordination between multiple network nodes to facilitate improvedreception from a UE. This involves efficient resource utilization andavoidance of high inter-cell interference. In particular, heterogeneousdeployments of small cells that are controlled by low power nodes suchas pico eNBs and remote radio heads (RRHs) are deployed within a macrocell such as 108. In a coordinated multi-point (CoMP) wirelesscommunication system, a UE receives signals from multiple base stations(eNB). These base stations may be macro eNB, pico eNB, femto eNB, orother suitable transmission points (TP). For each UE, a plurality ofchannel state information reference signal (CSI-RS) resources isconfigured based on which the UE can measure the downlink channel stateinformation. Each CSI-RS resource can be associated by the E-UTRAN witha base station, a remote radio head (RRH), or a distributed antenna. TheUE subsequently transmits to an eNB by an OFDM frame using allocatedphysical resource blocks (PRBs) in the uplink (UL).

Referring now to FIG. 2, there is a diagram of a heterogeneous wirelesscommunication system of the prior art. The system includes macro cells Aand B separated by cell boundary 200. Cell A is controlled by macro eNB202 and includes a pico cell 204 that is controlled by pico eNB 206.Cell B includes a pico cell 222 that is controlled by pico eNB 228 incommunication 226 with pico UE 224. Pico eNB 206 serves UEs such as picoUE 208 within region 204. Pico eNB 206 communicates with pico UE 208over data and control channels 210. Cell A also includes macro UE 214which communicates directly with macro eNB 202 over data and controlchannels 218. The introduction of pico eNB 206 within macro cell Aoffers cell or area splitting gain due to the creation of additionalcells within the same geographical area. Heterogeneous deployments canbe further classified as either shared or unique physical cell identity(PCID) scenarios. Referring to FIG. 2, in the shared PCID scenario, bothmacro eNB 202 and pico eNB 206 share the same PCID. Therefore, DLtransmission from both base stations to a UE can be made to appear asingle transmission from a distributed antenna system. Alternatively,pico eNB 206 may have a different unique PCID from macro eNB 202. Thesetwo scenarios result in different interference environments.

Uplink reference signals from a UE to an eNB are used to estimate theuplink channel state information. These reference signals includecontrol channel reference signals (RS), traffic channel demodulationreference signals (DMRS), and sounding reference signals (SRS). In LTEthe control and traffic channels are known as the Physical UplinkControl Channel (PUCCH) and Physical Uplink Shared Channel (PUSCH),respectively. Orthogonality of a reference signal within a cell ismaintained by using different cyclic shifts from a base sequence. Uplinkreference signals within the communication system are typicallymodulated with a constant amplitude zero autocorrelation (CAZAC)sequence or pseudorandom noise (PN) sequence. Different base sequences,however, are not orthogonal and require good network planning to achievelow cross correlation between adjacent cells. Inter-cell interference ismitigated by interference randomization techniques such as cell-specificbase sequence hopping and cyclic shift hopping patterns. Moreover,different problems arise depending on whether all cells within a CoMPcommunication system have a unique cell ID or share the same cell ID.

In a heterogeneous wireless communication system of prior art,inter-cell interference is significantly increased because of shortinter-site or inter-point distances. For UL cell selection it is better,in terms of reducing UL interference, for the UE to select the cell withthe lowest path loss. For example, macro UE 214 transmits uplink dataand control and also receives downlink control information on wirelessconnection 218 with macro eNB 202. However, the communication link 212between macro UE 214 and pico eNB 206 has a shorter path loss comparedto communication link 218. Thus, macro UE 214 generates significant ULinterference 212 to pico eNB 206 while trying to maintain acceptablelink quality with macro eNB 202. When macro UE 214 is near a cellboundary 200, it may also generate significant interference 220 for picoeNB 228. For the shared PCID scenario, all eNBs within the macro celleffectively form a super-cell comprising a distributed antenna system byvirtue of the single PCID. Therefore, there is little to no intra-cellinterference since transmitted reference signals are cyclic shifts ofthe same base sequence. On the other hand, area splitting gain cannot beobtained to take advantage of multiple deployed eNBs in the samegeographical area. For the unique PCID scenario, macro UE 214 maygenerate unacceptable UL interference to pico eNB 206. Conversely, picoeNB 206 degrades the DL reception of macro UE 214. Therefore, it isdesirable for macro UE 214 to be configured to transmit to pico eNB 206to reduce interference and also conserve battery life by lowering its ULtransmit power. Therefore, it can be observed that there is a tradeoffbetween increasing network capacity and mitigating the resultingincrease in inter-cell or inter-point interference.

While the preceding approaches provide steady improvements in wirelesscommunications, the present inventors recognize that still furtherimprovements in transmission of UL control information are possible.Accordingly, the preferred embodiments described below are directedtoward this as well as improving upon the prior art.

BRIEF SUMMARY OF THE INVENTION

In a preferred embodiment of the present invention, there is disclosed amethod of operating a wireless communication system. The method includesreceiving an identification parameter (ID) from a remote transmitter. Abase sequence index (BSI) and a cyclic shift hopping (CSH) sequence aredetermined in response to the received ID. A first pseudo-randomsequence is determined in response to the BSI. A subsequentpseudo-random sequence is selected in response to the CSH. The methodalso includes receiving a set of dedicated parameters from a remotetransmitter to determine the time/frequency region to transmit uplinkcontrol information or a sounding reference signal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a diagram of a wireless communication system of the prior art;

FIG. 2 is a diagram of a heterogeneous deployment of a wirelesscommunication system of the prior art showing a macro cell and two picocells;

FIG. 3 is a diagram of a wireless communication system of the presentinvention showing a macro cell and a pico cell deployed within the macrocell area with reduced inter-point interference;

FIG. 4 is a block diagram illustrating logical resource block allocationfor a macro cell and a pico cell as in FIG. 3;

FIG. 5 is a flow diagram showing sequence selection for soundingreference signals (SRS) and PUCCH reference signals (RS);

FIG. 6 is a flow diagram showing determination of PUCCH resource mappingto logical resource block based on cell-specific or UE-specific PUCCHparameters; and

FIG. 7 is a flow diagram of inter-eNB signaling to determine aUE-specific configuration of PUCCH and SRS transmission parameters.

DETAILED DESCRIPTION OF THE INVENTION

Inter-channel interference is a significant problem in the uplinkcontrol channel of an LTE wireless communication system.

The following abbreviations may be used throughout the instantspecification.

BLER: Block Error Rate

BSI: Base Sequence Index

CQI: Channel Quality Indicator

CRS: Cell-specific Reference Signal

CRC: Cyclic Redundancy Check

CSH: Cyclic Shift Hopping

CSI: Channel State Information

CSI-RS: Channel State Information Reference Signal

DCI: Downlink Control Indicator

DL: DownLink

DMRS: Demodulation Reference Symbol or UE-specific Reference Symbol

DPS: Dynamic Point Selection

eNB: E-UTRAN Node B or base station

EPDCCH: Enhanced Physical Downlink Control Channel

E-UTRAN: Evolved Universal Terrestrial Radio Access Network

HARQ-ACK: Hybrid Auto Repeat Request-Acknowledge

IRC: Interference Rejection Combining

JT: Joint Transmission

LTE: Long Term Evolution

MIMO: Multiple-Input Multiple-Output

MRC: Maximum Ratio Combining

PCFICH: Physical Control Format Indicator Channel

PCID: Physical Cell Identification

PDCCH: Physical Downlink Control Channel

PDSCH: Physical Downlink Shared Channel

PMI: Precoding Matrix Indicator

PRB: Physical Resource Block

PUCCH: Physical Uplink Control Channel

PUSCH: Physical Uplink Shared Channel

QAM: Quadrature Amplitude Modulation

RI: Rank Indicator

RNTI: Radio Network Temporary Indicator

RRC: Radio Resource Control

SNR: Signal to Noise Ratio

SRS: Sounding Reference Signal

TPC: Transmit Power Control

UE: User equipment

UL: UpLink

UpPTS: Uplink Pilot Time Slot

VCID: Virtual Cell Identifier

Embodiments of the present invention are directed to enhancing uplinkcontrol transmission on the PUCCH and sounding reference signaltransmission in a CoMP communication system. The present inventiondescribes methods for partitioning uplink control regions between cellssuch that inter-cell interference is minimized. A UE close to a cellboundary may generate severe UL interference in an adjacent cell due totransmission of non-orthogonal PUCCH reference signal base sequences inthe adjacent cells. The severity of the interference is proportional tothe difference in path loss between the UE to intended eNB and the UE toadjacent eNB. Here, path loss is a reduction in power density or signalattenuation with electromagnetic wave propagation. Referring to FIG. 3,according to one embodiment of the present invention for the case whereeach cell has a unique physical cell ID, pico eNB 206 measures receivedinterference partly due to macro UE 214. If the UL interference isgreater than a predetermined threshold, pico eNB 206 informs macro eNB202 on a backhaul link 216. One logical interface over which suchinter-eNB signaling takes place is an X2 interface. Subsequently macroeNB 202 directs macro UE 214 to adopt the PCID of pico cell 206 wheninitializing the pseudo-random sequence generators for generating theBSI and CSH sequences for PUCCH transmission. The macro UE 214 is nowconsidered a CoMP UE, wherein intra-cell orthogonality between UE 214and pico UE 208 is achieved and interference 212 (FIG. 2) is eliminated.One problem with this method, however, is that UE 214 determines itsresource block allocation for uplink control transmission based on itsserving cell's (macro eNB 202) PUCCH parameters. This may result inPUCCH resource allocation collisions between CoMP UEs and legacy UEswhen transmitting channel state information reports, schedulingrequests, and HARQ-ACK feedback. One solution to this problem is topartition uplink control transmissions from CoMP UEs and legacy UEs intodifferent RBs. This partitioning must be carefully managed to avoidincreasing PUCCH overhead.

In an alternative embodiment of the present invention where all cells ina CoMP coordination set share a common PCID, PUCCH area splitting gainis achieved by configuring UEs to transmit to the closest eNBs. Here,there is a trade off between increasing inter-point interference andarea PUCCH capacity. According to this embodiment, clusters of UEs thatare relatively close to each other and spatially isolated from otherclusters are assigned a unique ID for initializing a pseudo-randomsequence generator for the PUCCH reference signals and soundingreference signals. The new sets created by these UE clusters can beregarded as virtual cells and the dedicated ID is a correspondingvirtual cell ID (VCID).

Other exemplary usages of this concept of a virtual cell are possible.Referring to FIG. 3 an alternative embodiment is as follows. eNB 202configures macro cell A with PCID=123, pico eNB 206 configures its picocell with PCID=231 and pico eNB 228 configures its pico cell withPCID=55. A completely new virtual cell under the control of eNB 202 canbe created by configuring UE 214 with VCID n_(ID)=500.

Dynamic PUCCH resource allocation is considerably different fromsemi-static PUCCH resource allocation. Here, dynamic PUCCH resourceallocation is determined from DL scheduling assignments sent on thePDCCH or EPDCCH. The present invention utilizes existing parameters fromLTE Release 8-10 to calculate a single parameter m to map PUCCH resourceblocks (RBs) for both legacy and CoMP UEs. The concept taught by thepresent invention is a method of configuring UE-specific semi-static anddynamic PUCCH regions, where the former determines the semi-staticregion for transmitting CSI reports, scheduling requests, and HARQ-ACKfeedback due to semi-persistent scheduling, whereas the latterdetermines the region for dynamic HARQ-ACK feedback.

Referring now to FIG. 4, there is a diagram showing logical resourceblock allocation m for a macro cell and a pico cell as in FIG. 3. Theparameter m is increasing in the vertical direction as indicated. FIG. 4illustrates the case of resource block (RB) allocation where a macro UEis virtually transferred to a pico eNB. By virtual transfer we mean thatthe macro UE is configured as a CoMP UE to transmit uplink controlinformation to the pico eNB. The logical RB map for the macro UEconfiguration is shown on the left of FIG. 4. Each RB contains a groupof PUCCH resources, where the number of resources in a RB depends on thetype of PUCCH transmission. Blocks 400 through 406 represent the PUSCH,dynamic PUCCH format 1a/1b, semi-static PUCCH region for PUCCH formats1/1a/1b, and semi-static PUCCH region for PUCCH formats 2/2a/2b,respectively. The number of RBs allocated to PUCCH formats 2/2a/2bregion is denoted by N⁽²⁾ _(RB,m) while the starting offset for thedynamic PUCCH region is denoted by N⁽¹⁾ _(PUCCH,m). The logical RB mapfor the pico UE configuration is shown on the right with similardefinitions for the semi-static and dynamic PUCCH regions. Block 410represents PUSCH, block 414 the dynamic PUCCH format 1a/1b region, block416 the semi-static PUCCH format 1/1a/1b region and block 418 thesemi-static PUCCH format 2/2a/2b region. LTE Release 8-10 defines thePUCCH resource mapping to resource block m. A UE of these earlierreleases determines the starting offset of the dynamic PUCCH regionbased on the parameters N⁽²⁾ _(RB) and N⁽¹⁾ _(PUCCH).

A CoMP UE in a macro cell can be configured to transmit UL controlinformation in a CoMP dynamic PUCCH region depicted by block 412 of FIG.4. As such, the CoMP uplink control transmission to the pico eNB doesnot collide with the pico cell's native uplink control transmissions.However, if the CoMP UE is only provided with a new dedicated dynamicPUCCH offset parameter, denoted as N⁽¹⁾ _(PUCCH,UE), it shall use themacro's CSI region parameter N⁽²⁾ _(RB,m) as an initial offset asillustrated by the vertical arrow 420. In this case, the CoMP UE'sdynamic PUCCH transmission may collide with other dynamic PUCCHresources or even PUSCH transmission in the pico cell. Collisions arealso likely if a mixed RB exists, wherein one RB contains PUCCHresources for both HARQ-ACK feedback and CSI reports. Therefore,according to embodiments of the present invention both dynamic PUCCHoffset and CSI region parameters are provided to the UE.

Referring now to FIG. 5 a flow diagram is shown to illustrate how a UEdetermines the mapping of a PUCCH resource to a logical resource block.The UE receives an RRC message 500. If one or more dedicated PUCCHparameters from N⁽¹⁾ _(PUCCH,UE) and N⁽²⁾ _(RB,UE) are detected inmessage 500, the UE determines the PUCCH resource-to-RB mapping based onthe detected parameters 504. Otherwise, if RRC message 500 does notcontain one or more dedicated PUCCH mapping parameters, the UEdetermines the PUCCH resource-to-RB mapping based on the serving cell'scommon parameters of N⁽¹⁾ _(PUCCH) and N⁽²⁾ _(RB) as in 506.

In another embodiment of the present invention, a UE is configured witha dedicated ID, n_(ID), that is used for generating both a base sequenceindex (BSI) and a cyclic shift hopping (CSH) sequence for all PUCCHformats. The UE initializes a pseudo-random sequence generator usingeither the PCID or n_(ID). A binary flag is signaled to the UE toindicate whether the UE applies the PCID of the serving cell or appliesthe dedicated ID for generating the BSI and CSH sequence. The UE isfurther configured with dedicated UE-specific parameters N⁽¹⁾_(PUCCH,UE) and N⁽²⁾ _(RB,UE) to determine the starting offset of thedynamic PUCCH region.

Now referring to FIG. 6 a flow diagram is shown to illustrate how a UEgenerates the reference signal for PUCCH or SRS transmission. The UEmonitors for an RRC message 600. The UE determines in 602 if a detectedRRC message contains a dedicated PUCCH or SRS ID, n_(ID). If n_(ID) ispresent, the UE initializes the pseudo-random number generators 604 forthe base sequence group, sequence and cyclic shift hopping sequence withn_(ID). Otherwise, if n_(ID) is not detected in an RRC message the UEinitializes the pseudo-random sequence generators for the base sequencegroup, sequence and cyclic shift hopping sequence with the PCID 606 ofits serving cell. If block 608 determines that PUCCH is to betransmitted the UE selects in block 610 sequence 0 from the PUCCHsequence group and the cyclic shift corresponding to time slot n_(S).Otherwise if block 608 determines that SRS is to be transmitted the UEselects in 612 the sequence group and cyclic shift corresponding to thetime slot and corresponding SRS SC-FDMA symbol(s) within the time slot.At block 614, the UE generates the appropriate reference signal usingthe selected sequence.

CoMP enhancements can also be extended to SRS transmissions within aCoMP coordination area. For the shared PCID scenario, this enables anincrease in SRS capacity but at the cost of increased inter-cellinterference. Therefore, ensuring sufficient SRS capacity, whilemaintaining a reasonable SRS overhead per cell, becomes the primaryconcern as the number of served UEs increases within the CoMPcoordination area. Area splitting gain can be achieved by configuringUEs clustered around a reception point with a virtual cell ID for SRStransmission to the desired reception point. As a consequence ofintroducing a VCID for SRS transmission the present invention alsodescribes new mechanisms to improve SRS operation in a heterogeneousdeployment. One case is where more UEs are transmitting to a macro eNBthan to a pico eNB. Therefore, applying the same cell-specific SRSsubframe configuration across macro and pico cells unfairly penalizesPUSCH transmission efficiency in the pico cell due to PUSCH ratematching in a cell-specific SRS subframe. A different but related issueoccurs for decoupled data and control, wherein a UE receives PDCCH fromone eNB but transmits PUSCH to a different eNB. Thus, if the SRSsubframe configurations are different between the two cells, it needs tobe determined which of these configurations should be adopted by the UE.

An embodiment of the present invention is the configuration of adedicated UE-specific ID for SRS transmission. The UE determines thebase sequence group and sequence hopping patterns from the signaled SRSID.

Another embodiment of the present invention is that the UE is furtherconfigured with dedicated SRS parameters. For example, a macro UE can beconfigured with the cell-specific SRS parameters of a pico cell in orderto transmit SRS to the pico eNB. The UE can be configured with dedicatedparameters for the SRS subframe configuration, the SRS bandwidthconfiguration, and a parameter for enabling/disabling simultaneous SRSand HARQ-ACK transmission. For TDD systems a UE can further beconfigured with a parameter defining the maximum uplink pilot time slot(UpPTS) region.

Both open loop and closed loop UL power control are closely related toCoMP operation. This is because a wireless network may configure one setof transmission points for the DL of a UE and a different set ofreception points for the UL of a UE. Referring back to FIG. 3, forexample, UE 214 may be configured to send UL transmissions to pico eNB206 to minimize interference. However, UE 214 may still be configured toreceive DL transmissions from macro eNB 202. A problem of power controlarises when the path loss between UE 214 and pico eNB 206 issignificantly different from the path loss between UE 214 and macro eNB202. The UE may be UL power controlled such that the reception at thepico eNB is below a desired threshold. However, the macro eNB 202 maystill monitor UL transmissions from UE 214 for radio resource managementfunctions or for use in the DL in TDD systems where channel reciprocitybetween UL and DL can be exploited. Therefore, a reduction in power tojust satisfy a reception threshold at the pico eNB may degrade receptionat the macro eNB. This problem typically arises whenever transmissionpoints (TPs) and reception points (RPs) for a UE are not collocated. Onesolution to the problem is to provide separate power control loops forUL and DL. The first power control loop can be used for PUSCH, PUCCH andSRS transmissions to a nearby eNB. The second power control loop is usedto ensure reliable reception at a second eNB with a larger path loss tothe UE compared to the first eNB. This, however, creates other problemssuch as backwards compatibility with legacy systems. For example, a newmechanism is required for the eNB to signal independent transmit powercontrol (TPC) commands to a UE. SRS power control for LTE Release 10 isgiven by equation [1].P _(SRC,c)(i)=min{P _(CMAX,c)(i),P _(SRS) _(_) _(OFFSET,c)(m)+10 log₁₀(M_(SRS,c)(i))++P _(O) _(_) _(PUSCH,c)(j)+α_(c)(j),PL _(c) +f_(c)(i)}  [1]Here, P_(CMAX,c)(i) is the configured maximum transmit power of subframei for serving cell c. P_(SRS) _(_) _(OFFSET,c)(m) is a 4-bit parametersemi-statically configured by higher layers for m=0 and m=1 for servingcell c. Here, m is a trigger type to induce SRS transmission.M_(SRS,c)(i) is the bandwidth of the SRS transmission in subframe i forserving cell c. The current power control adjustment state of subframe ifor serving cell c is f_(c)(i). P_(O) _(_) _(PUSCH,c)(j) and α_(c)(j)are PUSCH reference power spectral density and fractional power controlparameters, respectively, for serving cell c. Here, j indicates the typeof PUSCH transmission, namely in response to a semi-persistent, dynamicor random access response grant. PL_(c) is the downlink path lossestimate calculated by the UE for serving cell c.

Another embodiment of the present invention resolves the foregoing powercontrol problem and maintains backwards compatibility with minimalimpact to the existing specification. According to this embodiment, theUE is configured by higher layer signaling to transmit aperiodic SRSwith offset P_(SRS) _(_) _(OFFSET)(1) for UL transmission. The UE isconfigured by higher layer signaling to transmit aperiodic SRS withoffset P_(SRS) _(_) _(OFFSET)(2) for DL transmission. The power controlparameters are separately substituted for a single power controlparameter and correspond to UL and DL power, respectively.

The present invention describes a method of signaling two or more powercontrol commands to a UE. The UE can be configured for aperiodic SRStransmission using dedicated power control commands in a group powercontrol signal that is transmitted on the PDCCH in a downlink controlinformation (DCI) format. The UE can be configured by RRC signaling withthe positions of two or more indexes in a bit map containing transmitpower control commands to a multiplicity of UEs. One TPC index indicatesa TPC command for a first power control loop and the other TPC indexindicates a TPC command for a second power control loop. Each TPC indexcan indicate a 1- or 2-bit TPC command. For example, in the LTE Release10 system a 2-bit command is transmitted in DCI format 3 while a 1-bitcommand is transmitted in DCI format 3A. When the CRC of the DCI formatis scrambled by a PUCCH RNTI, one TPC index can indicate the TPC commandfor the PUCCH whereas the other TPC index can indicate a TPC command foraperiodic SRS transmission. As a separate embodiment a set of one ormore indexes can be used to indicate different SRS TPC commands to theUE. Other variations are not precluded, the main idea being that a UE isconfigured with multiple indexes in a group power control DCI toindicate TPC commands for different power control loops.

The prior art for CoMP operation mainly targets scenarios whereinter-eNB signaling in a CoMP coordination area takes place over idealbackhaul links characterized by very high throughput and very lowlatencies on the order of less than 1-2 milliseconds. The embodiments ofthis present invention are also designed to work in deployments wherelatencies in inter-eNB signaling are on the order of at least tens ofmilliseconds. A base station may request over backhaul signaling (usinge.g. the X2 signaling protocol) that neighboring base stations transmittheir PUCCH configurations. Alternatively, a base station can signal,via the X2 logical interface, the PUCCH configuration of a cell underits control to one or more target cells controlled by other basestations. At a minimum the dynamic PUCCH offset parameter is indicatedin the PUCCH information element signaled on the backhaul link. Inaddition the number of RBs allocated for transmitting CSI reports can beindicated to allow a neighboring eNB to accurately determine theHARQ-ACK region for a cell controlled by a different eNB. Otherparameters may be optionally signaled including the number of PUCCHformat 1/1a/1b resources that can be assigned in one RB, the number ofcyclic shifts reserved for transmitting HARQ-ACK, and schedulingrequests in a resource block used for mixed transmission of HARQ-ACKscheduling requests and CSI.

In a different embodiment of the present invention the PUCCHconfiguration or some of the elements of this configuration can besignaled by a first base station when requested by a second basestation. In an alternate embodiment, a first base station may convey toa second base station a preferred PUCCH configuration for a neighboringcell under the control of the second base station.

For SRS transmission a first base station may indicate via e.g. the X2interface the SRS subframe configuration and SRS bandwidth configurationof a cell under its control to a second base station that controls aneighboring cell. The second base station may take this information intoaccount when configuring the neighboring cell's cell-specific SRSconfiguration and also the dedicated SRS configuration for a cell edgeUE in that cell. For example, referring to FIG. 3 eNB 202 can configuremacro cell A with a 5 ms periodicity for the cell-specific SRS subframesand a subframe offset of 0. Upon receiving this information, pico eNB206 can configure the pico cell with the same 5 ms periodicity but witha different subframe offset to avoid inter-cell interference. Inaddition for TDD systems a parameter defining the maximum UpPTS regioncan be signaled over a backhaul link such as the X2 interface.

Referring now to FIG. 7, an exemplary flow chart is shown describinginter-eNB signaling to enable network operation in a heterogeneousnetwork deployment. An eNB 702 controlling a cell serving UE 700transmits a request for the cell-specific PUCCH and/or SRS configurationof a neighboring cell under the control of eNB 704. The request message708 is transmitted over a backhaul link using the X2 signaling protocol.The eNB 704 sends a reply message 710 acknowledging the prior requestand also transmits the requested PUCCH or SRS configuration over thebackhaul link. The eNB 702 makes a decision 712 based on the receivedinformation from eNB 704 and on UE measurement report 706 on whether theUE should be configured to transmit PUCCH and/or SRS to eNB 704. If thedecision is positive, eNB 702 transmits an RRC configuration message 714to UE 700 with dedicated PUCCH or SRS parameters that match the PUCCH orSRS configuration of eNB 704. For PUCCH transmission UE 700 determinesthe RB mapping in 716 and transmits the required uplink controlinformation on PUCCH 718. For an aperiodic SRS request 720 targeting eNB704, the UE transmits the SRS 722 to eNB 704. Based on the UEmeasurement report 706 the eNB may alternatively determine in 712 thatUE 700 should continue to use the cell-common PUCCH or SRSconfiguration. In this case blocks 716, 718, 720 and 722 are performedaccording to the cell-common configuration of eNB 702.

Still further, while numerous examples have thus been provided, oneskilled in the art should recognize that various modifications,substitutions, or alterations may be made to the described embodimentswhile still falling with the inventive scope as defined by the followingclaims. Other combinations will be readily apparent to one of ordinaryskill in the art having access to the instant specification.

What is claimed is:
 1. A method of operating a wireless communicationapparatus, comprising: receiving a signal from a base station; selectinga cell-specific parameter in response to a first state of the signal, ora user-specific parameter in response to a second state of the signal,wherein the user-specific parameter is a virtual cell identificationparameter; initializing a first pseudo-random sequence generator forgenerating a base sequence with the virtual cell identificationparameter; initializing a second pseudo-random sequence generator forgenerating a cyclic shift hopping sequence with the virtual cellidentification parameter; generating an uplink reference signal inresponse to the selected parameter; and transmitting the uplinkreference signal generated from the base sequence and the cyclic shifthopping sequence.
 2. A method of operating a wireless communicationapparatus, comprising: receiving a signal from a base station;determining if a physical uplink control channel (PUCCH) or soundingreference signal (SRS) ID, n_(ID) is present in the signal; initializinga pseudo-random number generator for a base sequence group, sequence andcyclic shift hopping sequence with n_(ID) when n_(ID) is present in thesignal; initializing a pseudo-random number generator for a basesequence group, sequence and cyclic shift hopping sequence with aPhysical Cell Identification (PCID) associated with the base stationwhen n_(ID) is not present in the signal; selecting a cell-specificparameter in response to a first state of the signal or a user-specificparameter in response to a second state of the signal; and generating anuplink reference signal in response to the selected parameter.
 3. Amethod as in claim 2, wherein said signal from a base station is a RadioResource Control (RRC) signal.